Method of measuring axial force on a body utilizing two vibration modes of ultrasonic waves

Abstract

A method for measuring the axial force exerted on a body to be measured by applying two ultrasonic frequencies respectively having a transverse-wave vibration mode and a longitudinal-wave vibration mode to a body on which an axial force is exerted, measuring the natural frequencies of the body in the transverse-wave and longitudinal-wave vibration modes, obtaining the result of a computational operation (e.g., the result of a subtraction) on the measured natural frequencies, and measuring from this result the axial force exerted on the body in accordance with the predetermined result-versus-axial force calibration values.

What is claimed is: 
     
       1. In an axial force measuring method for measuring the axial force on a body to be measured by measuring the natural frequencies of said body through the forced oscillation thereof caused by ultrasonic waves and measuring the rate of change of said measured natural frequencies where a relationship (fε 2  - fε 1 )/fε 1  = K[{(1 -γε 2 ) √1 + ε 1  /(1 - ε 1 ) √1 + ε 2  }-1] (where γ is the Poisson's Ratio) is held between natural frequencies fε 1  and fε 2  of said body existing when a strain ε 1  (ε 1  ≧0) and another strain ε 2  (ε 2  > 0) are respectively produced in said body, said method comprising the steps of selecting a first ultrasonic frequency having a transverse-wave vibration mode for establishing K = 1 in said relationship and a second ultrasonic frequency having a longitudinal-wave vibration mode for establishing K>1 in said relationship, using said ultrasonic frequencies for respectively measuring the natural frequency of said body existing when an axial force is exerted thereon, performing a computational operation on said measured natural frequencies, and measuring the axial force exerted on said body from the result of said computational operation in accordance and with a predetermined result-versusaxial force calibration value. 
     
     
       2. A method according to claim 1, wherein the result of said computational operation is the difference between said measured natural frequencies. 
     
     
       3. A method according to claim 1, wherein the result of said computational operation is the value of rate of change between said measured natural frequencies. 
     
     
       4. A method according to claim 1, wherein said body to be measured is an automobile bolt.